1. Field of Invention.
This invention relates to a flexible coupling of the type utilized for interconnection between driving and driven rotating members where axial misalignment may be present.
2. Description of the Prior Art.
Flexible couplings of the general type to which the present invention pertains are well-known in the art and are illustrated, for example, in U.S. Pat. No. 3068,666 issued Dec. 3, l962 to George Sabadash, and U. S. Pat. No. 3,390,546 issued July 2, 1968 to Hollis Jewell. In the Sabadash patent, there is shown a flexible coupling utilizing a single helical beam between a pair of ends, and, in one embodiment, the beam has a rectangular cross-section with a depth greater than its thickness. In the Jewell patent, there is shown a flexible coupling with a plurality of helical beams, in which each of the helical beams extends less than three hundred and sixty degrees.
Devices according to each of these patents, while having wide-spread usage, are excessive in size and weight to compensate for improper cross-sectional geometry and/or material distribution by reason of the excess material, flexibility in such couplings is diminished. Such prior art couplings were all stronger when rotated opposite the direction of the helical spiral, the direction of rotation for which the coupling was primarily designed, than in the opposite direction of rotation. Consequently, either the coupling had to be rated differently according to the direction of rotation, or, if the coupling carried but a single rating, the rating was for a rotational direction in which the coupling could carry the smallest load. In certain instances, this problem was either ignored or not recognized in the prior art devices.
For a helical beam, because the beam length along the outer diameter is greater than the beam length along the inner diameter, for a constant thickness beam, failure in buckling normally will be initiated at the outer diameter. Such prior art couplings, in order to avoid failure of the buckling type, typically added material to the thickness of the beam, thereby decreasing the coupling flexibility and increasing the coupling weight. Height to thickness beam ratios of between 4 and 6 to 1 for such prior art couplings are typical.
If a large depth of thickness ratio for the coupling beam was used in order to increase the coupling flexibility when the coupling was rotated in the direction providing the greatest load carrying ability, predicting the load carrying capacity for such prior art couplings was complicated additionally. In such couplings, if a load was then applied in the opposite direction of rotation, a buckling type failure could occur at a load well below the elastic capability of the coupling.